RE: [sqlalchemy] Inheriting a functionality in SQLA
Yes, I tried mix-in approach, and it works, thanks.
From: sqlalchemy@googlegroups.com [mailto:sqlalchemy@googlegroups.com] On
Behalf Of Robert Forkel
Sent: 20 ноября 2012 г. 17:09
To: sqlalchemy@googlegroups.com
Subject: Re: [sqlalchemy] Inheriting a functionality in SQLA
As far as i know each declarative Base has its own metadata registry. You
are using two. Why not use multiple mixins to inherit the columns?
Am 20.11.2012 10:31 schrieb AlexVhr viho...@gmail.com:
I'm trying to incapsulate some functionality (some columns mainly) into base
classes to inherit my models from them. The setup looks like this:
class EntityTemplate():
@declared_attr
def __tablename__(cls):
return cls.__name__.lower()
id = Column(Integer(), primary_key=True)
timestamp = Column(DateTime())
class DocumentTemplate(EntityTemplate):
date = Column(Date())
number = Column(String(5))
Entity = declarative_base(cls=EntityTemplate, name='Entity')
Document = declarative_base(cls=DocumentTemplate, name='Document')
I'm trying to use it like this:
class Customer(Entity):
name = Column(String(25))
address = Column(String(50))
class Invoice(Document):
customer_id = Column(Integer, ForeignKey('customer.id'))
customer = relationship(Customer)
total = Column(Numeric(10,2))
Entity.metadata.create_all(engine)
Document.metadata.create_all(engine)
But on the last line I get this:
sqlalchemy.exc.NoReferencedTableError: Foreign key associated with
column
'invoice.customer_id' could not find table 'customer' with which to generate
a foreign key to target column 'id'
If I inherit Invoice from Entity instead of Document, everything is fine
(except the fact that columns date and number are missing). Why? (I'm using
SQLAlchemy-0.7.9-py3.2). Thanks!
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RE: [sqlalchemy] Inheriting a functionality in SQLA
Thanks for the clarification, it works now.
From: sqlalchemy@googlegroups.com [mailto:sqlalchemy@googlegroups.com] On
Behalf Of Michael Bayer
Sent: 21 ноября 2012 г. 3:58
To: sqlalchemy@googlegroups.com
Subject: Re: [sqlalchemy] Inheriting a functionality in SQLA
On Nov 20, 2012, at 4:31 AM, AlexVhr wrote:
I'm trying to incapsulate some functionality (some columns mainly) into base
classes to inherit my models from them. The setup looks like this:
class EntityTemplate():
@declared_attr
def __tablename__(cls):
return cls.__name__.lower()
id = Column(Integer(), primary_key=True)
timestamp = Column(DateTime())
class DocumentTemplate(EntityTemplate):
date = Column(Date())
number = Column(String(5))
Entity = declarative_base(cls=EntityTemplate, name='Entity')
Document = declarative_base(cls=DocumentTemplate, name='Document')
I'm trying to use it like this:
class Customer(Entity):
name = Column(String(25))
address = Column(String(50))
class Invoice(Document):
customer_id = Column(Integer, ForeignKey('customer.id'))
customer = relationship(Customer)
total = Column(Numeric(10,2))
Entity.metadata.create_all(engine)
Document.metadata.create_all(engine)
But on the last line I get this:
sqlalchemy.exc.NoReferencedTableError: Foreign key associated with
column
'invoice.customer_id' could not find table 'customer' with which to generate
a foreign key to target column 'id'
If I inherit Invoice from Entity instead of Document, everything is fine
(except the fact that columns date and number are missing). Why? (I'm using
SQLAlchemy-0.7.9-py3.2). Thanks!
the use of two different declarative_base() makes this more complicated as
there is no common MetaData collection between the two classes which allows
foreign keys to be resolve based on string names, as well as class names
like Customer to be resolved. the Base + MetaData combination represent a
pair of registries that allow these string lookups to work.
So using one declarative base would solve the issue, else you need to forego
the usage of string identifiers and pass object references instead:
customer_id = Column(Integer, ForeignKey(Customer.id))
customer = relationship(Customer)
but there's really no need to use two different declarative bases, your
EntityTemplate and DocumentTemplate are mixins, which if you'd like them to
be packed into a single base class can be accomplished using a subclass of a
single Base with the __abstract__ = True flag.
http://docs.sqlalchemy.org/en/rel_0_8/orm/extensions/declarative.html#abstra
ct
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Re: [sqlalchemy] Inheriting a functionality in SQLA
As far as i know each declarative Base has its own metadata registry. You
are using two. Why not use multiple mixins to inherit the columns?
Am 20.11.2012 10:31 schrieb AlexVhr viho...@gmail.com:
I'm trying to incapsulate some functionality (some columns mainly) into
base classes to inherit my models from them. The setup looks like this:
class EntityTemplate():
@declared_attr
def __tablename__(cls):
return cls.__name__.lower()
id = Column(Integer(), primary_key=True)
timestamp = Column(DateTime())
class DocumentTemplate(EntityTemplate):
date = Column(Date())
number = Column(String(5))
Entity = declarative_base(cls=EntityTemplate, name='Entity')Document =
declarative_base(cls=DocumentTemplate, name='Document')
I'm trying to use it like this:
class Customer(Entity):
name = Column(String(25))
address = Column(String(50))
class Invoice(Document):
customer_id = Column(Integer, ForeignKey('customer.id'))
customer = relationship(Customer)
total = Column(Numeric(10,2))
Entity.metadata.create_all(engine)Document.metadata.create_all(engine)
But on the last line I get this:
sqlalchemy.exc.NoReferencedTableError: Foreign key associated with
column'invoice.customer_id' could not find table 'customer' with which to
generate
a foreign key to target column 'id'
If I inherit Invoice from Entity instead of Document, everything is fine
(except the fact that columns date and number are missing). Why? (I'm
using SQLAlchemy-0.7.9-py3.2). Thanks!
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Re: [sqlalchemy] Inheriting a functionality in SQLA
On Nov 20, 2012, at 4:31 AM, AlexVhr wrote:
I'm trying to incapsulate some functionality (some columns mainly) into base
classes to inherit my models from them. The setup looks like this:
class EntityTemplate():
@declared_attr
def __tablename__(cls):
return cls.__name__.lower()
id = Column(Integer(), primary_key=True)
timestamp = Column(DateTime())
class DocumentTemplate(EntityTemplate):
date = Column(Date())
number = Column(String(5))
Entity = declarative_base(cls=EntityTemplate, name='Entity')
Document = declarative_base(cls=DocumentTemplate, name='Document')
I'm trying to use it like this:
class Customer(Entity):
name = Column(String(25))
address = Column(String(50))
class Invoice(Document):
customer_id = Column(Integer, ForeignKey('customer.id'))
customer = relationship(Customer)
total = Column(Numeric(10,2))
Entity.metadata.create_all(engine)
Document.metadata.create_all(engine)
But on the last line I get this:
sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column
'invoice.customer_id' could not find table 'customer' with which to generate
a foreign key to target column 'id'
If I inherit Invoice from Entity instead of Document, everything is fine
(except the fact that columns date and number are missing). Why? (I'm using
SQLAlchemy-0.7.9-py3.2). Thanks!
the use of two different declarative_base() makes this more complicated as
there is no common MetaData collection between the two classes which allows
foreign keys to be resolve based on string names, as well as class names like
Customer to be resolved. the Base + MetaData combination represent a pair of
registries that allow these string lookups to work.
So using one declarative base would solve the issue, else you need to forego
the usage of string identifiers and pass object references instead:
customer_id = Column(Integer, ForeignKey(Customer.id))
customer = relationship(Customer)
but there's really no need to use two different declarative bases, your
EntityTemplate and DocumentTemplate are mixins, which if you'd like them to be
packed into a single base class can be accomplished using a subclass of a
single Base with the __abstract__ = True flag.
http://docs.sqlalchemy.org/en/rel_0_8/orm/extensions/declarative.html#abstract
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